Friction disks for a clutch traditionally comprise a so-called “progressive” torque input web carrying peripheral friction linings.
Two guide washers arranged on either side of the web are mounted on a central hub integral with the driven shaft of the gearbox, capturing compression springs in intercalated receptacles.
Torque transmission, and filtering of engine irregularities, is accomplished by successive compression and relaxation of the springs.
When the clutch pedal is actuated the clutch mechanism releases the friction linings, causing disconnection of the driving shaft from the driven shaft of the gearbox.
Torque transmission must be as progressive as possible during the re-engagement phase.
This is because during this phase, the linings are heavily loaded and tend to deform in an uncontrolled manner, which then creates discontinuities in torque transmission which are accompanied by a chattering phenomenon, with jolts that are very uncomfortable and prejudicial to driving of the vehicle.
Applied-blade progressivity devices, such as the one described in FR 2 352 211, already exist.
This document discloses a clutch friction disk comprising a progressivity device whose central web carries on its periphery a series of coplanar blades integrated with the web by rivets and intended to support a first friction lining, a second lining being fastened on the opposite face of the central progressivity web.
These blades exhibit at least two pleats of material, delimiting between them the support region of the first lining and mechanically compensating, by compression, for the deformations of that lining in order to keep the two linings in parallel planes.
These pleats extend on either side of the fastening region of the blades on the web, being oriented along intersecting lines that are inclined with respect to its diametrical axis.
This configuration is not always satisfactory, however, since it does not allow effective resolution of the technical problems referred to above.
Specifically, because the rivets that provide connection between the web and the first lining via the blades exert radial traction forces on that lining, and because, during re-engagement, the inclined pleats are subjected to compressive stresses in divergent directions, the resultant of those forces still causes the appearance on that lining of geometric defects such as out-of-parallelism, which generate chattering.
In addition, when the pleats are compressed, the support region tends to deform in an excessive and uncontrolled fashion, forming a cup whose base comes into abutment against the progressivity web of the friction disk; this causes stiffening of the progressivity curve and prevents the stiffness specifications from being achieved.
FR 2 530 756 and DE 21 11 892 describe progressivity blades applied and riveted onto the external rim of a web, the lining support region of which has cutouts that allow said blades to be lighter and more flexible.
These cutouts nevertheless do not allow the deformation of the support regions to be controlled, and the profile and geometry of those regions are furthermore inappropriate for solving the out-of-parallelism problems of the linings.